In a telecommunications network, a switch is a device that channels incoming data from any of a plurality of input ports to at least one output port that will communicate the data toward its intended destination. In the traditional circuit-switched telephone network, one or more switches are used to set up a dedicated temporary connection or circuit for an exchange between two or more parties. On an Ethernet local area network (LAN), a switch determines which output port to forward a particular packet frame based on the medium access control (MAC) address of the received packet frame. In a packet switched IP network, a switch may determine which output port to use to route the network packet based on the IP address of each packet.
Various software algorithms and applications have been developed to discover the topology of a network and detect the presence of loops in a network. Whenever a loop is detected, the traffic on those ports that form the loop may be blocked. A blocked port may not be used to forward traffic since it would result in the forwarded traffic being looped back and subsequently received at the output port from which it was communicated. Standardized protocols such as spanning tree and rapid spanning tree are utilized to detect and prevent occurrences of loops within a network. Such methods for detecting and preventing loops may be referred to as active methods.
A loop generally creates a high concentration of traffic, which excludes other applications from communicating data over the input and output ports that form the loop. If a sufficient amount of switch ports are placed in a loop, this may render the switch inoperable. This may occur in instances where traffic in a loop is also being broadcasted to other ports and may reduce those portions of a network that is served solely by the switch.
Quality of Service (QoS) is an IP concept and uses tools and protocols that are designed to aid the provision of defined predictable data transfer characteristics. Quality of Service is also relevant at layer 2 within the Ethernet environment and also within the WAN technologies such as Frame Relay and ATM. The drive for QoS has become very strong in recent years because there has been a growth of multimedia traffic such as voice and video, which mixes it with more traditional data traffic such as file transfer protocol (FTP), Telnet and server message block (SMB). Applications such as Voice over IP (VoIP) and various conferencing applications, for example, Microsoft's Netmeeting have opened up the possibility of more interactive communications between users not just over a LAN but also over a WAN.
While data traffic such as text may be tolerant of delays and dropped packets, voice traffic is very sensitive to and therefore, very intolerant of delays. Video is also intolerant of jitter and packet loss, plus it has the added complication of being very bursty at times. This convergence of multimedia traffic with traditional data traffic is set to grow and therefore requires methods and tools to ensure that providers may deliver networks that give the users confidence to use these tools effectively.
There may be a plurality of problems associated with providing a QoS for a network, for example, there may be a shortage of bandwidth because network links are oversubscribed. The packets may be lost due to congestion at bursty periods. There may be an end-to-end delay comprising for example, a fixed switch delay as packets are layer 2 switched from the call initiator, a fixed encoding delay, a fixed voice activity detection (VAD) around 5 ms, a fixed packetization delay, a variable output queuing delay as voice packets enter an output queue and wait for the preceding frame to be played out, and a fixed serialization delay for the time it takes to get the bits on to the circuit. The end-to-end delay may also comprise a fixed processing delay for the time it takes for the packets to be examined, routed, and managed, a variable network queuing delay due to clocking frames in and out of the different network switches, a fixed network propagation delay as the packets traverse the medium, a variable input queuing delay as voice packets enter an input queue and wait for the preceding frame to be played out, a fixed dejitter buffer delay, a fixed switch delay as packets are layer 2 switched to the endpoint, a fixed decoding delay.
High bandwidth multimedia applications may be introduced to a data network that has a well designed core and access topology, particularly if the core is based on Gigabit Ethernet technology and the access switches are not over-subscribed with respect to the backbone links. Even in this scenario there is the issue of speed mismatches between technologies such as Gigabit Ethernet and Fast Ethernet. This requires buffering and therefore leads to a requirement to queue and prioritize traffic. Layer 2 switches may mark frames using Class of Service (CoS) marking if end devices do not mark the frames themselves. These frames may then be assigned to hardware queues that exist on modern layer 2 switches. The most significant network bottlenecks exist at the remote access points, the WAN access, Internet access and the servers. Many of the technologies involved in QoS deal with how packets are dealt with as they enter and leave a network because merely adding more bandwidth at the edge is only a short term solution that just resolves capacity and perhaps some congestion problems. Adding bandwidth does not resolve jitter or add any traffic prioritization features.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.